MATLAB: Provided a 1D array of integers, find all combinations of 3 values from this set such that: a+b+c=0

arrayshomeworkthree sumvectors

Ok, I can't figure out where I what I am doing wrong in my code. I have tried debugging but without knowing what they are asking me to fix it's kind of hard to just go from that. Any advice on how to correct this would be greatly appreciated.

function [S] = ThreeSum(i, j, k)
    for i=0;
        i < S;
        for j = i + 1;
            j < S;
                for k = j + 1;
                    k < S;
                        if a(i) + a(j) + a(k) == 0;
                        end
                end
        end
    end
end

Best Answer

if A is your 1D array, than you can use:

B=combntns(A,3);

C=sum(B,2);

D=B(~C,:);

Related Solutions

MATLAB: How to check if the next generated row has no repetitions in the same columns in the previous row using a while loop

Your problem is that the check you add in the end, (s (:, j)) ~ = 1, examines if the sum in column j is more than 1 - but the index in which you add your 1 is a random index between 1 and 15. So the event you wish to avoid can very easily happen in column 14 while you are checking column 1. In addition, because your while loop runs until a mistake is found and then stops - it does not correct the mistake that caused it to exit.

Here is my suggestion:

w = [3,2,4,6];    %% quantities of elements
zw = sum(w); 
s = zeros (numel(w),zw); %% initial "empty" matrix
for k=1:numel(w)
    for j=1:zw
         while sum(s(k,:))<w(k) && sum(sum(s))<zw  %move the third condition down
             
             rando=randi(15); %log which index you insert the most recent 1 in
             s(k,rando) = 1;
             
             if sum(s(:,rando))~=1  %if that most recent 1 caused your column sum to exceed 1, undo it. 
                 s(k,rando)=0;
             end
 
         end  %and the while loop will keep running, until you have w(k) 1's in the k'th row. 
    end
end

MATLAB: What is wrong with the for loop

elements = 4;

s=3; %size of matrix nxn

k=[1 1 1; 1 1 1; 1 1 1];

length = (s* elements) - (elements-1);

K = zeros(length,length);

for j = 0:elements-1

index =(1:s);

n = index + j*(s-1);

K(n,n) = k(1:s,1:s);

end

for i = 1:elements-1

K(((i*s)-(i-1)), ((i*s)-(i-1))) = k(1,1)+k(s,s);

end

This does exactly what I want I answered my own question nevermind. Here it is for reference.

Best Answer

Related Solutions

MATLAB: How to check if the next generated row has no repetitions in the same columns in the previous row using a while loop

MATLAB: What is wrong with the for loop

Related Question